The present invention relates to a semiconductor device of the compounds of III-V groups and a method for surface treatment of such compounds.
As LED for high luminance light emission consisting of AlGaAs semiconductor, LED of single hetero junction structure or double hetero junction structure has been conventionally used which has higher carrier injection efficiency, higher output and higher response speed than the homo-junction structure LED.
These hetero-junction structure LEDs are characterized in that Al.sub.x Ga.sub.l-x As having high AlAs mixed crystal ratio is used on the light emitted side. For example, in the epitaxial growth of the substrate for red light emitting high luminance LED, Zn-doped Al.sub.0.75 Ga.sub.0.25 As layer is formed by 200 .mu.m (p-type) on p-type GaAs substrate [(100) surface] as p-clad layer by liquid growth method. Then, Zn-doped Al.sub.0.35 Ga.sub.0.65 As layer is formed by 2-3 .mu.m (p-type) as p-active layer. Further, Te-doped Al.sub.0.75 Ga.sub.0.25 As layer is formed by about 50 .mu.m as n-clad layer. Using GaAs substrate selective etchant, optical absorption GaAs substrate is removed to obtain high luminance LED chip. The mixed crystal ratio of chip surface is as high as 0.75. Al.sub.x Ga.sub.l-x As layer with such high AlAs mixed crystal ratio is very easily oxidized. This results in easy deterioration of light emitting characteristics and the shorter service life of the element. The same applies to the resin-sealed element.
To overcome this problem, a method to form SiNx film has been proposed.
Also, it has been proposed to provide surface roughness in order to increase the external quantum efficiency by preventing total reflection on the surface.
In the past, however, it has been customary only either to provide the surface roughness or to form SiNx film. When only the surface roughness are provided, there arise the problems of moisture resistance and shorter service life of the element due to surface oxidation. When only SiNx film is furnished as protective film, bond strength is weak and film is easily detachable.